Septum extraction electrode comprising a plurality of parallel wires under tension



Nov. 7, 1967 K. STEIMEL 3,351,793

SEPTUM EXTRACTION ELECTRODE COMPRISING A PLUHALITY 0F PARALLEL WIRES UNDER TENSION Filed Oct. 25, 1965 F r r t (L T I a 1l HUI] MECHANICAL OSCILLATOR Inventor:

Ko'xL Steimel.

fittovnass v United States Patent 0 L 3 Claims. Cl. 313-62) ABSTRACT 0F THE DISCLGSURE For use in a cyclotron, a deflecting condenser composed of a plurality of tensioned Wire portions extending perpendicular to the direction of movement of the cyclotron beam and arranged to undergo an oscillatory motion in the direction of their length so as to vary the point at which the cyclotron beam strikes each element, thus permitting the condenser to be exposed to high power beams.

The present invention relates to a device for use in a cyclotron, and particularly to a septum, or deflecting condenser, for causing a stream, or beam, of accelerated particles to exit from a cyclotron.

Various techniques are already known for deflecting the beam from a cyclotron so as to cause it to exit therefrom, one such technique inVOlVing the extraction of the beam by means of the electric field of a suitably formed deflecting condenser or septum. The prior art devices of this type generally comprise two elongated electrodes which are spaced opposite each other and at a given distance apart.

The prior art septa are invariably arranged to have an inner electrode which lies in the current region of the cyclotron, and which is thus struck by a stream of particles present in the cyclotron. This arrangement has been found to possess the drawbacks of reducing the intensity of the cyclotron beam and of causing the septum to eX- perience appreciable heating. Consequently, the inner electrode becomes bent and hence begins to act as an extremely high catching resistance for the exiting particle stream. Experience has shown that the inner electrode be comes considerably eroded at the point where it is first struck by the stream, thereby producing a distortion of the electric field. The over-all result is a great loss of particles and a deterioration of the optical characteristics of the beam.

It is therefore a primary object of the present invention to overcome the above-noted drawbacks.

It is a more specific object of the present invention to provide a septum which is capable of supporting extremely high specific loads and which does not experience the above-noted difficulties.

According to the present invention, an improved septum is achieved by forming its inner electrode, which is to be exposed to the beam, to have a plurality of elements, which are preferably constituted by thin wires, oriented substantially perpendicular to the plane of movement of the particles forming the beam.

According to one novel feature of the invention, these elements are arranged to undergo a continuous motion in the direction of their length so as to continuously vary the point at which the beam strikes each element.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings in which:

of FIGURE 1, so

FIGURE 1 is a schematic illustration of a cyclotron equipped with a septum.

FIGURE 2 is a side view of an electrode constituting the inner electrode of a prior art septum indicated in FIGURE 1.

FIGURE 3 is a side view of an improved inner elec trode according to the present invention.

Referring first to FIGURE 1, there is shown a cyclotron having a main septum constituted by electrodes 1 and 2. In the case where the electron beam 3 is constituted by positive ions, the outer electrode 2 is at a negative high voltage potential and the inner electrode 1 is grounded. The beam 3 passes between the two electrodes.

FIGURE 2 shows an inner electrode 1 according to the prior art, which electrode may be made of tungsten. The prior art septum having an electrode as shown in FIGURE 2 presents several serious drawbacks. The most difficult problem associated with such a septum resides in the fact that the inner electrode 1, which lies in the current region of the cyclotron, is struck by the stream of particles produced by the cyclotron. This causes a loss in beam intensity and an appreciable heating of the electrode. Consequently, the inner electrode 1 becomes bent and begins to act as an extremely high catching resistance for the stream of particles. Experience has shown that the electrode 1 becomes considerably eroded at the point where it is first struck by the particle stream, thereby resulting in a distortion of the electric field.

Turning now to FIGURE 3, there is shown an inner electrode 1' for a septum constituting a. preferred embodiment of the present invention. This electrode is shown to include a large number of wires 4 which are for example, each bent to have a U-shaped, or hairpin, configuration. The two free ends of each bent wire 4 are attached, by soldering or welding for example, to a strut 5 of a frame whose other strut 6 is provided with a plurality of springs 7 each of which engages the bend of a respective one of the Wires 4. The pull exerted by each spring 7 acts to place the wires 4 under tension. The wires 4 can be made, for example, of tungsten, the diameter of the wires being approximately 50p and the wires being spaced from each other by a distance of about 1 mm.

The electrode 1' shown in FIGURE 3 is positioned in the cyclotron in the manner shown for the electrode 1 that the individual wires 4 are positioned at right angles to the plane in which the particles in the cyclotron stream move, this plane being parallel to the plane of FIGURE 1.

Because the inner electrode of FIGURE 3 is constituted by a series of individual wires 4, each producing an electric field, the composite electric field along the electrode will have a somewhat periodic nature. However, by maintaining the distance between the wires 4 small with respect to the separation between the electrodes 1 and 2, the periodic nature of the field of the electrode 1' has a negligible etfect on the operation of the unit.

According to another feature of the present invention, special provision is made for the case where the electrodes are to be subjected to extremely high loads. In particular, the septum can be mounted so that, for high loads, the inner electrode 1' is moved in such a manner that the point at which the beam will impinge on wires 4 will be continuously varied. This may be accomplished, for example, by mounting the entire septum 1'2 on a unit which causes it to oscillate in a direction parallel to the axis of the cyclotron, this direction being indicated by the double arrow 9 of FIGURE 3.

Such an arrangement is shown in FIGURE 3 wherein the struts 5 and 6 are mounted on a post 14 which is disposed on a mechanical oscillating unit 15. This unit may be constituted by any well known type of device for producing mechanical oscillations, such as the movable core of an A.C. excited solenoid, or a motor driving a cam or a plate to which the post 14 is eccentrically coupled.

The electrode 1 of FIGURE 3 can also be constructed to have a series of closed wire loops in place of the hairpin wires of FIGURE 3. Each of these loops can be disposed between a pair of rollers which are continuously driven so as to cause a continuous movement of the wires which will cause the straight portions thereof to advance in the direction of the arrow of FIGURE 3. Thus, the movement of the wire loops will have the same effect as the previously-described oscillation of the entire septum. Arrangements of this type can be given a very small length, as short as 1 cm. for example, and can also be used to constitute an input septum which functions to deflect a portion of the beam produced by the cyclotron in order to reduce the load on the output septum to a sufliciently small value. In order to obtain maximum effectiveness, such an input septum, which is shown as a septum 11, 12 in FIGURE 1, is preferably arranged in the path of the beam at a position 90 ahead of the main septum, which angle is taken about a circle whose center coincides with the axis of the cyclotron.

It may thus be seen that, in accordance with the present invention, a septum electrode having a plurality of thin wires is provided together with suitable means for 50 moving the electrode that the point at which the cyclotron beam strikes the wires is continuously varied.

It may also be seen that, in further accordance with the present invention, there is provided an additional septum which is arranged on the path of the cyclotron beam approximately 90 ahead of the main septum for reducing the load to which the main septum will be subjected.

It will be understood that the above description of the present invention is susceptible to various modifications, changes, and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What is claimed is:

1. For use in a septum for extracting the beam from a cyclotron, an inner electrode to be exposed to the beam and comprising a plurality of elements each constituted by a wire placed under mechanical stress and oriented substantially perpendicular to the plane of movement of the particles forming the beam, said wires being in pairs, each of which pairs is constituted by a single piece of wire in the form of a hairpin, said electrode further comprising a holder to which the free ends of each hairpin are attached, and resilient means engaging the bend of each of said hairpins for maintaining said hairpins under tension.

2. An arrangement as defined in claim 1 further comprising an additional septum arranged in the path of said beam at a point ahead of said electrode, with respect to the direction of movement of the beam, and at an angle of to said electrode with respect to a circle centered on the axis of the cyclotron.

3. For use in a septum for extracting the beam from a cyclotron, an inner electrode to be exposed to the beam and comprising a plurality of elements oriented substantially perpendicular to the plane of movement of the particles forming the beam, and driving means to which said electrode is connected for causing said wires to move in a direction parallel to their axes for causing the point at which the cyclotron beam strikes each of said wires to be continuously varied.

References Cited UNITED STATES PATENTS 2,467,390 4/1949 Kelley 313-278 X 2,586,494 2/1952 Wideroe 313-62 X 2,626,351 1/1953 Powell 313-62 X 2,789,221 4/1957 Tobias 313-62 X 2,954,497 9/1960 Rishell 313-350 3,177,393 4/1965 Gerlach et al. 313-278 JAMES \V. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner. 

1. FOR USE IN A SEPTUM FOR EXTRACTING THE BEAM FROM A CYCLOTRON, AN INNER ELECTRODE TO BE EXPOSED TO THE BEAM AND COMPRISING A PLURALITY OF ELEMENTS EACH CONSTITUTED BY A WIRE PLACED UNDER MECHANICAL STRESS AND ORIENTED SUBSTANTIALLY PERPENDICULAR TO THE PLANE OF MOVEMENT OF THE PARTICLES FORMING THE BEAM, SAID WIRES BEING IN PAIRS, EACH OF WHICH PAIRS IS CONSTITUTED BY A SINGLE PIECE OF WIRE IN THE FORM OF A HAIRPIN, SAID ELECTRODE FURTHER COMPRISING A HOLDER TO WHICH THE FREE ENDS OF EACH HAIRPIN ARE ATTACHED, AND RESILIENT MEANS ENGAGING THE BEND OF EACH OF SAID HAIRPINS FOR MAINTAINING SAID HAIRPINS UNDER TENSION. 